If you know a secret the rest of the world doesn't, it can drive you nuts. From dealing with little white lies to exposing a sexual harasser, consider how, when—and when not—to let the cat out of the bag.

Secrets are like stars: They're hot, volatile concentrations of energy, and they have two ways of dying. Over time, small stars simply burn out and cool off, becoming what astronomers call white dwarfs. Massive stars collapse in on themselves, growing so dense that they create an immense gravitational vortex from which even light can't escape. They become black holes.

You've probably felt the difference between a "little white lie" and what I think of as a black hole secret, the kind that absorbs and darkens everything around it. In her book Anatomy of a Secret Life: The Psychology of Living a Lie, Gail Saltz, MD, describes how even a relatively minor lie, such as cheating on a tax form, exerts a powerful gravitational force on the liar, whose attention is focused on not talking about what they've done. Secret keepers may become uncommunicative, withdraw from others, exhibit strange moods, even isolate themselves completely.

The problem is even worse for people who don't have black hole secrets but are holding such confidences for others. Secret keeping is immensely stressful; it has well-documented effects on things like immune function and even longevity. I've found that these three questions can help determine whether a secret is a white dwarf or a black hole.